Re: [PATCH 2/3] KVM: x86: Save&restore interrupt shadow mask

Marcelo Tosatti
2010-02-17T14:54:51Z

On Wed, Feb 17, 2010 at 11:10:07AM +0200, Gleb Natapov wrote:
> On Wed, Feb 17, 2010 at 10:03:58AM +0100, Jan Kiszka wrote:
> > >
> > > Also, as Avi mentioned it would be better to avoid this. Is it not
> > > possible to disallow migration while interrupt shadow is present?
> >
> > Which means disallowing user space exists while the shadow it set? Or
> > should we introduce some flag for user space that tells it "do not
> > migration now, resume the guest till next exit"?
> >
> I think disabling migration is a slippery slope. Guest may abuse it. May
> be it will be hard to do with interrupt shadow, but the mechanism will be
> used for other cases too. I remember there was an argument that we
> should not migrate while vcpu is in a nested guest mode.

Agree that guest may abuse it. Better to save/restore
blocking-by-sti/by-mov-ss individually.

I was thinking the writeback of interrupt shadow / interruptibility state
would be too complicated (eg necessary to care about ordering, etc), but
now i see its handled in kernel (inject_pending_event and friends).